- "Love doesn't exist. There is no such thing as love. Therefore, there's no sorrow."
Satan is the hidden main antagonist of Devilman Crybaby. They are an angel who was banished to Earth following a fallout with God. Under the care of Psycho Jenny, they took the form of a human boy named Ryo Asuka who had befriended a young Akira Fudo. Years later, they planned to destroy humanity by turning them against each other by revealing the presence of demons.
As Ryo Asuka, he is a lean young man with blonde hair cut into the shape of a bowl, as well as piercing blue eyes. He is always seen in white clothes including a large overcoat.
As Satan, they are displayed as an intersex being with breasts, but male groin area. Their blonde hair grows longer and becomes wavy. Wearing no clothes, their body is covered in a veil of light. All around their body are pairs of white wings that appear on their back, the back of their feet, and the back of their head.
As Ryo Asuka, he is shown to be a young man who follows logic to its most extreme. This includes mercy killing for anything that can't be saved, as well as breaking several Japanese laws such as owning and using a gun and driving with an American driver's license to have a better survival chance. After an encounter with demons, Ryo had strove to expose demons in the best way possible to ensure humanity's survival. Ryo is also willing to kill anyone to protect Akira's secret as Devilman as he did with Koji Nagasaki and his mother.
Ryo himself did not believe in love or suffering, being rather apathetic to them after his banishment as Satan. His encounter with Akira and his kindly demeanor however showed his more vulnerable side as he fell in love with Akira. They had bottled up all of their frustrations of the unfortunate realities he had faced. As Ryo, he had come to grips with his grief and strove to create a better world free of the demons and regardless of the number of lives lost. But even then, he knew his actions would have dire consequences, giving Akira a choice before going any further in their plans. They only time he had ever shown fear was against the flash of light caused by God that wiped out an American Navel Fleet.
As Satan, their version of a better world is revealed to be through the lense of a spoiled child and/or a Social Darwinist, the eradication of humanity seeing them as a weak species. While having no love for demons as a whole, their more simplistic lifestyles were better in their eyes seeing as their adaptations made better chances for survival. The Devilmen themselves however were seen as an unintended consequence that he planned only for Akira. Satan also revealed their love for Akira, going out of their way to prevent his death by making him strong enough.
Satan, as Ryo, has known Akira since early childhood and the two formed a close and valued friendship. Through Akira, Ryo came to learn about human emotions, like love and kindness. Ryo fell in love with Akira over their friendship, to the point that he spurs Akira's possession, and the events of the series, in hopes of Akira being able to survive the impending apocalypse. Akira is the only person Ryo has ever cared about, and losing Akira at the end of the series causes him to completely break down.
As Ryo he earned a Ph.D at a young age and even taught classes. He was an accomplished driver and mechanic, driving a modified sports car to keep up with a demon and using to hold his equipment. He carries an assortment of guns including a machine gun, an anti-material sniper rifle, and a pistol. Ryo also had an unnatural healing factor, able to heal and recover from serious injuries that would have crippled regular humans (although, this may be because he is an angel). He is also a keen manipulator, able to control people and events to the point of total domination.
As Satan, they are able to reincarnate at any place and time. Ever since their incarnation as a male human child, he displayed abilities such as making plants grow, killing animals with thought, causing water to materialize, create force fields, and powerful telekinetic force. Once fully revealed, they are able to fire powerful beams of light that can tear the moon in half. They can also summon lightning bolts to attack certain areas.
Satan had went against God's cold and bitter regime, later being banished to Earth in its prehistoric time. There, he encountered the demons, finding their simplistic but brutal ways interesting. However, when God had its forces attack Earth to wipe out the demons and restart from scratch, Satan and the demons would continue to thrive. In Satan's case, he would reincarnate.
Satan was born into a Peruvian native village, as the strangely skinned and haired boy. As his powers manifested, he came to be worshipped as a god to the point of sacrifice and heart offering. One day, a military unit attacked the village with Satan knocked into the ocean. He ended up floating and washed up on a dock in a village with Japanese people in it where he met the young Akira.